Low Energy Direct Contact Membrane Desalination: Conjugated Heat and High Fidelity Flow Simulation

Abstract

The steady state performance of Low Energy Direct Contact Membrane Distillation (DCMD) is numerically investigated. A case of uniform flow is considered entering both the feed side at a temperature above the permeate side. The developed fluid model is governed by the Navier-Stokes flow and energy equation in a coupled conjugate heat transfer formulation to the flow and the solid membrane. Across the membrane and depending on the membrane parameters including permeability, thickness, pore size and conductivity the local temperature difference creates a driving pressure gradient responsible of evaporation part of the feed adjacent to the membrane surface, transport it through the pores, and condense it at permeate side through the hydrophobic membrane. The membrane's coefficients of DCMD membrane is evaluated along with the mass flux, heat flux, temperature polarization factor, and thermal efficiency. In this paper, two flow configurations are studied: Counter and Parallel flow. A parametric study is conducted incorporating velocity combinations and concluding an optimum configuration in terms of DCMD efficiency, mass flux. In view of these plausible results, a sensitivity study to the flow rates is carried out to gain better insight to the temperature polarization, heat flux including convective, conductive and the associated latent heat as well as in understanding its effect on the process metrics and yield.